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I think that the latest version fixes the bug that people were encountering going from 1.6 to 1.8.x. But prior to that it was safest to go from 1.6 to 1.7.x, then to 1.8.x. Read this article for a general over view of how and what to do:http://www.tmib.net/how-upgrade-osticket-17st-172

Having SSH access means if you are comfortable running commands at a command prompt that you could skip download and uploading and simply grab the file from the server (presuming that you have wget), unpack it, etc.

If you have any specific questions please feel free to ask here, and I will respond when I see it.

You're problem is probably stemming from the fact that you are running an Italian version of osTicket that was not released by osticket.com. You would definitely want to make a back up of your database before you tried to do something like that.